Sequence conservation around the 5' ends of the larval serum protein 1 genes of Drosophila melanogaster.

We have determined the nucleotide sequence at the 5' ends of the genes for the alpha, beta and gamma polypeptides of larval serum protein 1 (LSP1) of Drosophila melanogaster. In their upstream regions, the three genes share homology around the TATA boxes. There is also a homologous region of about 20 nucleotides at positions 200, 216 and 377 upstream from the alpha, beta and gamma genes, respectively. Another 18-nucleotide homology occurs between a sequence 111 nucleotides upstream from the alpha gene and 130 nucleotides upstream of the beta gene. This contains a seven-nucleotide match with a sequence 180 nucleotides upstream from the gamma gene. The sequences corresponding to the 5' non-translated regions of the RNA show two regions of strong homology: one being within the first 20 nucleotides at the very 5' end of the RNA, and the other being between nucleotides 27 and 52 of the three transcripts. The first AUG codon to precede a long open reading frame is found at nucleotides 89, 86 and 83 downstream from the 5' end of the alpha, beta and gamma RNAs, respectively. An extremely conserved nucleotide sequence with an exact homology of 66 nucleotides between the alpha and beta genes, and sharing 27 nucleotides with the gamma gene, is contained within this long open reading frame in the first exon. Conceptual translation of the long open reading frame shows that the hydrophobic nature of the first 20 amino acids of the three polypeptides has been conserved whereas the exact sequence has not. This suggests that the N termini contain signal sequences required for secretion of the protein into the haemolymph. The three genes have intervening sequences ranging from 65 to 68 nucleotides in length at comparable locations close to the 5' end of the genes.